Cancer is a disease characterized by the rapid uncontrolled growth of cells that are able to invade nearby tissues, as well as metastasize to other areas of the body. Several methods for cancer treatment are employed today. These include systemic treatments such as chemotherapy, hormone therapy or biological therapy, and local treatments such as surgery, cryosurgery, or radiotherapy.
Radiotherapy is an important treatment for many types of cancer. Recent advances in radiotherapy have provided finer control over the distribution of radiation dose delivered to subjects' tissues. This fine control can be exploited to permit radiation to be delivered to a lesion such as a tumor while sparing normal tissue that is closely adjacent to the tumor. Imaging is an important adjunct to radiotherapy. Imaging is used to identify the extent of lesions that may be treated by radiotherapy as well as to determine the location of the lesion relative to other nearby anatomical structures. Imaging is also used to monitor the response of a subject to treatment.
The use of radiotherapy is not limited to cancer treatment. Radiotherapy can also be useful in the treatment of other conditions.
Image-guided radiation therapy (IGRT) is a technique that involves acquiring images during a course of radiation therapy. IGRT can deliver radiation with improved accuracy by taking into account changes in the subject as revealed by the images. Images may be taken before or during the delivery of radiation. Some radiation sources, such as linear accelerators are equipped with imaging systems such as kV X-ray imagers for acquiring images of a subject while the subject is positioned for the delivery of radiation.